Maspin is an epithelial-specific serine protease inhibitor (serpin) with tumor suppressive function. Exogenously added maspin inhibits tumor cell invasion and motility in vitro. In comparison, in vivo data show that maspin inhibits tumor metastasis. Also, exogenous addition of maspin, in vivo, decreases angiogenesis. Maspin expression is correlated with a better clinical prognosis in many cancers, such as prostate and breast. Unfortunately, maspin expression is often down regulated or lost as the tumor progresses to a metastatic carcinoma. Maspin is an intracellular protein as well as an extracellular protein. Extracelluar maspin regulates pro-urokinase plasminogen activator (pro-uPA), and its receptor, uPAR, at the cell surface. Interestingly, uPA, and uPAR are both up regulated in tumor progression and high expression of uPA has been associated with a poor clinical prognosis. Extracellular maspin may exert its tumor suppressive role, at least in part, by blocking uPA activation. However, the mechanism in which extracellular maspin regulates pro-uPA has yet to be identified. Identification of the mechanism of maspin regulation may provide insight into a novel therapeutic strategy. The hypothesis for the project is that extracellular maspin acts as a regulator of the tumor microenvironment. To address this hypothesis, there are three specific aims. Specific Aim 1 is to investigate whether the mechanism of maspin secretion determines its biological function as a regulator of the tumor microenvironment. Specific Aim 2 is to investigate whether the uPA/uPAR complex may be necessary for maspin-mediated cell-cell communication in the tumor microenvironment. Specific Aim 3 is to investigate the biological consequences of extracellular maspin upon internalization.